For allowing users to operate keyboards in a dark or dim environment, some keyboards with light sources such as light emitting diodes (LED) have been introduced into the market. The light sources may provide light beams to illuminate the keyboards. The keyboards with the illuminating functions are also referred as illuminated keyboards. By using the illuminated keyboards, the users can easily identify the characters or the symbols marked on the keys of the illuminated keyboards.
FIG. 1 is a schematic cross-sectional view illustrating a conventional illuminated keyboard. As shown in FIG. 1, the conventional illuminated keyboard 10 comprises plural key structures 11, a membrane switch board 12, a backlight module 13, and a base plate 14. For clarification and brevity, only one key structure 11 is shown in FIG. 1. The membrane switch board 12 comprises an upper wiring plate 15, a lower wiring plate 16, and a partition plate 17. The backlight module 13 comprises a light guide plate 18, a flexible circuit board 19, and a light source L.
The key structure 11 is disposed over the membrane switch board 12 to be depressed by the user. When the key structure 11 is depressed, the membrane switch board 12 is electrically conducted to generate a key signal. The detailed structure of the membrane switch board 12 will be illustrated as follows.
In the membrane switch board 12, the upper wiring plate 15 comprises an upper circuit layer 151, and the lower wiring plate 16 comprises a lower circuit layer 161. The upper circuit layer 151 and the lower circuit layer 161 are circuit patterns, which are made of electrically-conductive material. The upper wiring plate 15 is disposed over the lower wiring plate 16. The partition plate 17 comprises plural perforations 171. Moreover, the partition plate 17 is arranged between the upper wiring plate 15 and the lower wiring plate 16 for preventing erroneous contact between the upper wiring plate 15 and the lower wiring plate 16.
As the key structure 11 is depressed, the upper wiring plate 15 is subjected to deformation. Consequently, the upper circuit layer 151 of the upper wiring plate 15 is penetrated through the corresponding perforation 171 of the partition plate 17, and the upper circuit layer 151 of the upper wiring plate 15 is contacted with the lower circuit layer 161 of the lower wiring plate 16. Under this circumstance, the electrical connection between the upper circuit layer 151 and the lower circuit layer 161 results in the key signal.
The backlight module 13 is disposed under the membrane switch board 12 for illuminating the key structure 11. The backlight module 13 comprises the light guide plate 18, the flexible circuit board 19, and the light source L. The light source L is disposed on the flexible circuit board 19. Moreover, the flexible circuit board 19 comprises a light source circuit layer (not shown) for driving the light source L. The light guide plate 18 is located at a side of the light source L for transferring the light beam which is emitted by the light source L. The base plate 14 is disposed under the backlight module 13 for supporting the key structure 11, the membrane switch board 12 and the backlight module 13.
By means of the light source L and the light guide plate 18, the light beam from the light source L can be uniformly transferred to each key structure 11. Consequently, the illuminated keyboard 10 has the backlighting function, and the number of the light sources L is reduced. Under this circumstance, the illuminated keyboard 10 is power-saving and cost-effective.
However, the conventional illuminated keyboard 10 still has some drawbacks. For example, since the light source L and the light guide plate 18 have inherent thickness, the arrangement of the light source L and the light guide plate 18 under the membrane switch board 12 may increase the overall height of the illuminated keyboard 10. As known, it is difficult to further reduce the thickness of the illuminated keyboard 10.
Therefore, there is a need of providing an improved illuminated keyboard in order to eliminate the above drawbacks.